Silicon light-receiving device

ABSTRACT

A silicon light-receiving device is provided. In the device, a substrate is based on n-type or p-type silicon. A doped region is ultra-shallowly doped with the opposite type dopant to the dopant type of the substrate on one side of the substrate so that a photoelectric conversion effect for light in a wavelength range of 100-1100 nm is generated by a quantum confinement effect in the p-n junction with the substrate. First and second electrodes are formed on the substrate so as to be electrically connected to the doped region. Due to the ultra-shallow doped region on the silicon substrate, a quantum confinement effect is generated in the p-n junction. Even though silicon is used as a semiconductor material, the quantum efficiency of the silicon light-receiving device is far higher than that of a conventional solar cell, owing to the quantum confinement effect. The silicon light-receiving device can also be formed to absorb light in a particular or large wavelength band, and used as a solar cell.

BACKGROUND OF THE INVENTION

This application claims the benefit of Korean Patent Application No.2002-7707, filed on Feb. 9, 2002, in the Korean Intellectual PropertyOffice, the disclosure of which is incorporated herein in its entiretyby reference.

1. Field of the Invention

The present invention relates to the field of silicon light-receivingdevices, and more particularly, to a silicon light-receiving devicehaving a high quantum efficiency due to a quantum confinement effect.

2. Description of the Related Art

FIG. 1 is a schematic diagram of a solar cell as an example of a siliconlight-receiving device. Referring to FIG. 1, a general solar cell has ap-n diode structure in which an n-type semiconductor 1 and a p-typesemiconductor 2 are joined to obtain and utilize a photovoltaic effectby which light energy is converted into electric energy. Electrodes 3and 4 for connecting an external circuit to the n- and p-typesemiconductors 1 and 2 are formed on the upper surface of the p-typesemiconductor 2 and the bottom surface of the n-type semiconductor 1,respectively.

Referring to FIG. 2, when light is incident upon the p-n diode structureof FIG. 1 and a photon is absorbed into it, a pair of an electron 7 aand a hole 7 b is generated at both sides of a p-n junction. At thistime, the electron 7 a moves toward the n-type semiconductor 1 and thehole 7 b moves in the opposite direction. Accordingly, when the loadresistor 5, which is an external circuit, is connected to the p-n diodestructure, according as light energy is converted into electric energy,current I flows through the p-n diode structure.

Typically, silicon is used as the semiconductor material for solar cellsas described above. The solar cells having a diode structure usingsilicon semiconductors provide a low efficiency when converting lightenergy into electric energy. In theory, single crystal silicon has about23% photoelectric conversion efficiency, polycrystal silicon has about18% photoelectric conversion efficiency, and amorphous silicon has about14% photoelectric conversion efficiency. During actual operation ofsolar cells using one of the aforementioned types of silicon assemiconductor materials, the photoelectric conversion efficiencydecreases more.

SUMMARY OF THE INVENTION

To solve the above-described problem, it is an object of the presentinvention to provide a silicon light-receiving device providing farhigher quantum efficiency than a conventional solar cell because of aquantum confinement effect generated at a p-n junction even thoughsilicon is used as a semiconductor material.

To achieve the object, embodiments of the present invention provide asilicon light-receiving device including a substrate, a doped region,and first and second electrodes. The substrate is based on n-type orp-type silicon. The doped region is doped to an ultra-shallow depth withthe opposite type dopant to the dopant type of the substrate on one sideof the substrate. Thus, a photoelectric conversion effect for light in awavelength range of 100-1100 nm is generated by a quantum confinementeffect in the p-n junction with the substrate. The first and secondelectrodes are formed on the substrate so as to be electricallyconnected to the doped region.

Preferably, micro-cavities of various sizes are formed so that thesilicon light-receiving device is used as a solar cell for absorbinglight of various wavelengths in the range of 100 to 1100 nm.

It is also preferable that the silicon light-receiving device furtherincludes a control film formed on one side of the substrate. The controlfilm serves as a mask when the doped region is formed and helping thedoped region to be formed to the ultra-shallow depth.

The control film may be formed of silicon oxide SiO₂ to a properthickness that enables the doped region to be formed to theultra-shallow depth.

Preferably, the doped region is formed by non-equilibrium diffusion ofthe dopant. The dopant may be one of boron and phosphorus.

It is also preferable that at least one of a quantum well, a quantumdot, and a quantum wire, in each of which electron-hole pairs arecreated, is formed at the p-n junction of the doped region with thesubstrate.

Preferably, the sub-band energy levels within at least one of thequantum well, the quantum dot, and the quantum wire are changed by theapplication of external voltage so that an absorption light wavelengthband is changed.

The substrate may be formed of one of Si, SiC, and diamond.

BRIEF DESCRIPTION OF THE DRAWINGS

The above and other features and advantages of the present inventionwill become more apparent by describing in detail exemplary embodimentsthereof with reference to the attached drawings in which:

FIG. 1 is a schematic diagram of a solar cell as an example of aconventional silicon light-receiving device;

FIG. 2 is a schematic diagram of the photoelectric conversion principlein the p-n diode structure of FIG. 1;

FIG. 3 is a schematic diagram of a silicon light-receiving deviceaccording to an embodiment of the present invention;

FIG. 4A shows the structure of a p-n junction when a doped region isformed very thinly by non-equilibrium diffusion;

FIG. 4B shows the energy bands of longitudinal and lateral quantum wells(QW) formed at the p-n junction of FIG. 4A by non-equilibrium diffusion;

FIG. 5 is a schematic diagram of a silicon light-receiving deviceaccording to another embodiment of the present invention;

FIG. 6 shows the photoelectric conversion principle in a siliconlight-receiving device according to an embodiment of the presentinvention; and

FIG. 7 is a graph showing a comparison of the external quantumefficiency (EQE) of a conventional solar cell using single crystalsilicon semiconductors with the EQE of a silicon light-receiving deviceaccording to the present invention, when it serves as a solar cell.

DETAILED DESCRIPTION OF THE INVENTION

Referring to FIG. 3, a silicon light-receiving device according to anembodiment of the present invention includes a substrate 11, a dopedregion 15 formed on one side of the substrate 11, and first and secondelectrodes 17 and 19 formed on the substrate 11 so as to be electricallyconnected to the doped region 15. Preferably, the siliconlight-receiving device according to embodiments of the present inventionfurther includes a control film 13 formed on one side of the substrate11 in order to serve as a mask upon formation of the doped region 15 andcontrol the doped region 15 to be formed to a desired ultra-shallowthickness. The control film 13 can be selectively removed after thedoped reaion 15 is formed.

The substrate 11 is formed of a semiconductor material including silicon(Si), for example, Si, silicon carbide (SiC), or diamond, and doped withn-type dopant.

The doped region 15 is doped with the opposite type dopant to thesubstrate 11, i.e., p+ type dopant, by implanting a dopant (e.g., boronor phosphorous) through the opening of the control film 13 into thesubstrate 11 using the non-equilibrium diffusion technique.

Preferably, the doped region 15 is doped to a desired ultra-shallowdepth so that at least one of a quantum well, a quantum dot, and aquantum wire is formed at the boundary between the doped region 15 andthe substrate 11, that is, at the p-n junction 14 and a consequentquantum confinement effect enables light with a wavelength ranging from100 to 1000 nm, preferably, from 200 to 900 nm, to be converted intoelectric energy with a high quantum efficiency.

Here, a quantum well is generally formed at the p-n junction 14.Alternatively, either a quantum dot or a quantum wire can be formed atthe p-n junction 14. Two or more of the quantum well, the quantum dot,and the quantum wire can also be formed at the p-n junction 14.Hereinafter, the case where a quantum well is formed at the p-n junction14 will be described for simplicity. Accordingly, even though it isdescribed hereinafter that a quantum well is formed at the p-n junction14, it must be considered that at least one of the quantum well, thequantum dot, and the quantum wire is formed.

FIG. 4A shows the structure of the p-n junction 14 when the doped region15 is formed to an ultra-shallow depth by non-equilibrium diffusion.FIG. 4B shows the energy bands of longitudinal and lateral quantum wells(QW) formed at the p-n junction 14 of FIG. 4A by non-equilibriumdiffusion. In FIG. 4B, reference character Ec denotes a conduction bandenergy level, reference character Ev denotes a valence band energylevel, and reference character Ef denotes a Fermi energy level. Theseenergy levels are well known in the field of semiconductor-relatedtechnology, so they will not be described in detail.

As shown in FIGS. 4A and 4B, the p-n junction 14 has a quantum wellstructure in which different doped layers alternate. Here, a well and abarrier are approximately 2 nm, 3 nm.

Such ultra-shallow doping to form a quantum well at the p-n junction 14can be achieved by optimally controlling the thickness of the controlfilm 13 and the conditions of diffusion.

During diffusion, the thickness of a diffusion profile can be controlledto, for example, 10-20 nm, by an appropriate diffusion temperature andthe deformed potential of the surface of the substrate 11. In such anultra-shallow diffusion profile, a quantum well system is created. Here,the potential of the surface of the substrate 11 is deformed by thethickness of the control film 13 at its initial stage and a surfacepretreatment, and the deformation becomes worse as diffusion progresses.

Preferably, the control film 13 is a silicon oxide film SiO2 having aproper thickness that enables the doped region 15 to be formed to anultra-shallow depth. For example, the control film 13 is formed to havea mask structure by forming a silicon oxide film on one side of thesubstrate 11 and etching the silicon oxide film using photolithographyto obtain an opening for diffusion.

As well known in the field of diffusion technologies, if the siliconoxide film is thicker than the proper thickness (for example, severalthousand Å) or a diffusion temperature is low, vacancy mainly affectsdiffusion and deep diffusion occurs. If the silicon oxide film isthinner than the proper thickness or a diffusion temperature is high, Siself-interstitial mainly affects diffusion and deep diffusion occurs.Accordingly, when the silicon oxide film is formed to a proper thicknessthat enables Si self-interstitial and vacancy to be created at similarpercentages, the Si self-interstitial and vacancy are combined togetherso that diffusion of a dopant is counteracted. Thus, ultra-shallowdoping is possible. The physical properties of the Si self-interstitialand vacancy are well known in the technical field relating to diffusion,so they will not be described in detail.

Alternatively, the substrate 11 may be doped with p-type dopant, and thedoped region 15 may be doped with n+-type dopant.

For connection with an external circuit, the first electrode 17 isformed on the upper surface of the substrate 11 on which the dopedregion 15 is formed, and the second electrode 19 is formed on the bottomsurface of the substrate 11. FIG. 3 shows an example where the firstelectrode 17 is formed of an opaque metal so as to partially contact theouter side of the doped region 15. The first electrode 17 can be formedof a transparent electrode material, such as indium tin oxide (ITO), onthe entire surface of the doped region 15.

Instead of forming the second electrode 19 on the bottom surface of thesubstrate 11, the first and second electrodes 17 and 19 can be formed onthe side of the substrate 11 that has the doped region 15, as shown inFIG. 5. The same reference numerals of FIG. 5 as those of FIG. 3 referto the same elements actually performing the same functions, so theywill not be described again.

In a silicon light-receiving device according to the present inventionas described above, a quantum well is formed at the p-n junction 14between the doped region 15 and the substrate 11. As shown in FIG. 6,the quantum well absorbs incident light to generate a pair of anelectron and a hole. In FIG. 6, reference numeral 31 denotes a quantumwell, reference numeral 33 denotes a sub-band energy level, referencecharacter “e” denotes an electron, reference character “h” denotes ahole, and reference character “p” denotes a photon. Also, a referencecharacter Ev denotes a valence band energy level, and a referencecharacter Ec denotes a conduction band energy level.

As shown in FIG. 6, when light is incident upon the p-n junction 14 andthe p-n junction 14 with a quantum well structure absorbs the photon p,the electron e and the hole h are each excited to the sub-band energylevel within the quantum well formed at the p-n junction 14.Accordingly, if an external circuit, such as a load resistor 18 of FIGS.3 and 5, is connected, current proportional to the amount of radiatedlight flows.

The wavelength of absorption in such a silicon light-receiving deviceaccording to exemplary embodiments of the present invention isdetermined according to micro-cavities due to micro-defects generated onthe surface of the substrate 11 (actually on the surface of the dopedregion 14). By adjusting the size of the micro-cavity based on themanufacturing process, the absorption wavelength in the siliconlight-receiving device according to the present invention may bedetermined to be a particular wavelength existing in the range of100-1100 nm or may vary.

When micro-cavities are formed to have a uniform size, the siliconlight-receiving device according to the present invention absorbs lightwith a specific wavelength and converts the absorbed light into electricenergy. When the micro-cavities have various sizes, the siliconlight-receiving device according to the present invention absorbs lightof a large wavelength band, such as, a range of 100-1100 nmcorresponding to the absorption range of a general solar cell,preferably, a wavelength band of 200-900 nm, and converts the absorbedlight into electric energy.

The micro-cavities are created from deformed potential due tomicro-defects formed on the surface of the doped region 14. Hence, aquantum well can be deformed by adjusting the deformed potential, andconsequently the micro-cavities are determined. Accordingly, the sizesof the micro-cavities are controlled to cause absorption in the specificor large wavelength band.

As a result, a silicon light-receiving device according to the presentinvention is formed to have micro-cavities of uniform size, so that itcan be used to detect light with a particular wavelength.

In addition, the silicon light-receiving device according to the presentinvention is formed to have micro-cavities of various sizes that canabsorb light with a large wavelength band including the absorptionwavelength band of a general solar cell, such as 100-1100 nm,preferably, 200-900 nm, so that it can be used as a solar cell.

FIG. 7 is a graph showing a comparison of the external quantumefficiency (EQE) of a conventional solar cell using single crystalsilicon semiconductors with the EQE of a silicon light-receiving deviceaccording to the present invention, when it serves as a solar cell.Referring to FIG. 7, in the wavelength band of 200-900 nm, the averageEQE of the silicon light-receiving device according to the presentinvention is about 50-60%, while the conventional solar cell formed ofsingle crystal silicon has an EQE of no more than 35%. Here, thewavelength band of 200-900 nm is generally used to calculate theefficiency of a solar cell.

As can be seen from FIG. 7, in case that a silicon light-receivingdevice according to the present invention is manufactured to serve as asolar cell, the efficiency of the silicon light-receiving deviceaccording to the present invention is much greater than that of aconventional solar cell.

To be more specific, in a conventional solar cell where a doped regionis formed on a silicon substrate using a general doping method, light isabsorbed and scattered on a p-type or n-type doped layer and accordinglycannot be annihilated by an electron-hole pair that is output to avertical electrode and contributes to a response. Also, the conventionalsolar cell has an indirect band gap structure in which only lightabsorbed by a depletion layer under the doped layer is detected as acurrent signal without quantum effect, thus providing low detectionefficiency.

On the other hand, the ultra-shallow doped region 15 of the siliconlight-receiving device according to the present invention generates aquantum confinement effect due to a local change in a chargedistribution potential, thus providing high quantum efficiency. Inparticular, as shown in FIG. 6, the sub-band energy level 33 is formedwithin the quantum well 31, so that light can be detected with highefficiency.

The silicon light-receiving device according to the present inventionhaving the ultra-shallow doped region 15 provides an excellentsensitivity, for example, in a light wavelength band of 100-1100 nm.

In addition, the silicon light-receiving device according to the presentinvention can move the entire absorption wavelength band by changing thesub-band energy level of a quantum well according as external voltage isapplied.

To be more specific, voltage can be applied to the first and secondelectrodes 17 and 19 in order to control the interval between sub-bandenergy levels within a quantum well formed at the p-n junction 14. Ifthe first and second electrodes 17 and 19 are formed as shown in FIG. 2,voltage can be vertically applied. If the first and second electrodes 17and 19 are formed as shown in FIG. 5, voltage can be horizontallyapplied.

As described above, when the silicon light-receiving device according tothe present invention is subjected to horizontal or vertical voltage,the sub-band energy levels within the quantum well formed at the p-njunction 14 can be changed to move the entire absorption wavelengthband.

A silicon light-receiving device according to the present invention asdescribed above has an ultra-shallow doped region on a siliconsubstrate, so that a quantum confinement effect is generated at a p-njunction even though silicon is used as a semiconductor material. Owingto the quantum confinement effect, the quantum efficiency of the siliconlight-receiving device according to the present invention is far higherthan that of a conventional solar cell.

Such a silicon light-receiving device according to the present inventioncan be formed to absorb light in a particular or large wavelength band,and used as a solar cell.

In addition, the silicon light-receiving device according to the presentinvention can move the absorption wavelength band by changing thesub-band energy level within at least one of a quantum well, a quantumdot, and a quantum wire according as external voltage is applied.

While the present invention has been particularly shown and describedwith reference to exemplary embodiments thereof, it will be understoodby those of ordinary skill in the art that various changes in form anddetails may be made therein without departing from the spirit and scopeof the present invention as defined by the following claims.

1. A silicon light-receiving device comprising: a substrate based onn-type or p-type silicon; a doped region doped to an ultra-shallow depthwith the opposite type dopant to the dopant type of the substrate on oneside of the substrate, wherein the death is selected so that aphotoelectric conversion effect for light in a wavelength range of100-1100 nm is generated by a quantum confinement effect in the p-njunction with the substrate; and first and second electrodes formed onthe substrate so as to be electrically connected to the doped region. 2.The silicon light-receiving device of claim 1, wherein micro-cavities ofvarious sizes are formed so that the silicon light-receiving device isused as a solar cell for absorbing light of various wavelengths in therange of 100 to 1100 nm.
 3. The silicon light-receiving device of claim2, further comprising a control film formed on one side of thesubstrate, the control film serving as a mask when the doped region isformed and helping the doped region to be formed to the ultra-shallowdepth.
 4. The silicon light-receiving device of claim 1, furthercomprising a control film formed on one side of the substrate, thecontrol film serving as a mask when the doped region is formed andhelping the doped region to be formed to the ultra-shallow depth.
 5. Thesilicon light-receiving device of claim 3, wherein the control film isformed of silicon oxide SiO₂ to a proper thickness that enables thedoped region to be formed to the ultra-shallow depth.
 6. The siliconlight-receiving device of claim 1, wherein the doped region is formed bynon-equilibrium diffusion of the dopant.
 7. The silicon light-receivingdevice of claim 6, wherein the dopant includes one of boron andphosphorus.
 8. The silicon light-receiving device of claim 1, wherein atleast one of a quantum well, a quantum dot, and a quantum wire, in eachof which electron-hole pairs are created, is formed at the p-n junctionof the doped region with the substrate.
 9. The silicon light-receivingdevice of claim 8, wherein the sub-band energy levels within at leastone of the quantum well, the quantum dot, and the quantum wire arechanged by the application of external voltage so that an absorptionlight wavelength band is changed.
 10. The silicon light-receiving deviceof claim 1, wherein the substrate is formed of one of Si, SiC, anddiamond.